Shielded electrical contact and doping through a passivating dielectric layer in a high-efficiency crystalline solar cell, including structure and methods of manufacture

ABSTRACT

Solar cell structures and formation methods which utilize the surface texture in conjunction with a passivating dielectric layer to provide a practical and controllable technique of forming an electrical contact between a conducting layer and underlying substrate through the passivating dielectric layer, achieving both good surface passivation and electrical contact with low recombination losses, as required for high efficiency solar cells. The passivating dielectric layer is intentionally modified to allow direct contact, or tunnel barrier contact, with the substrate. Additional P-N junctions, and dopant gradients, are disclosed to further limit losses and increase efficiency.

RELATED APPLICATION INFORMATION

This Application claims priority from U.S. Provisional PatentApplication Ser. No. 61/318,099, filed Mar. 26, 2010. This Applicationis also related to PCT Application Serial No. PCT/US2010/031869, filedApr. 21, 2010, which was published on Oct. 28, 2010, as InternationalPublication No. WO 2010/123974 A1, and which claims priority from U.S.Provisional Application Ser. No. 61/171,194, filed Apr. 21, 2009, andentitled “High-Efficiency Solar Cell Structures and Methods ofManufacture.” Each of these Applications is hereby incorporated hereinby reference in its entirety. All aspects of the present invention maybe used in combination with the disclosures of the above-notedApplications.

TECHNICAL FIELD

The present invention relates to solar cells. More particularly, thepresent invention relates to improved solar cell structures and methodsof manufacture for increased cell efficiency.

BACKGROUND OF THE INVENTION

Solar cells are providing widespread benefits to society by convertingessentially unlimited amounts of solar energy into useable electricalpower. As their use increases, certain economic factors becomeimportant, such as high-volume manufacturing and efficiency.

With reference to the schematic views of exemplary solar cells of, e.g.,FIGS. 1-2 below, solar radiation is assumed to preferentially illuminateone surface of a solar cell, usually referred to as the front side. Inorder to achieve a high energy conversion efficiency of incident photonsinto electric energy, an efficient absorption of photons within asilicon wafer is important. This can be achieved by a low parasiticoptical absorption of photons within all layers except the wafer itself.Surface texturization is a well known technique for improved capture ofthe incident light radiation. Texturization may be effected in severalways, but most commonly formed using a wet acid or alkaline etch, inwhich the surface of the wafer etches non-uniformly, leaving a densefield of pyramids or conical-spikes over the entire surface of the solarcell substrate. However, it is understood that the geometrical shapeand/or surfaces may be textured in any shape beneficial for improvedsolar cell efficiency.

An important parameter for high solar cell efficiency is surfacepassivation. Surface passivation is generally considered to effect thesuppression of recombination of electrons and holes at or in thevicinity of certain physical surfaces of the wafer. Surfacerecombination can be reduced by the application of dielectric layersover the substrate. These layers reduce the interface density of statesand therefore reduce the number of recombination centers. The mostprominent examples are thermally grown silicon oxide and PECVD depositedsilicon nitride. Other examples of surface passivating layers includeintrinsic amorphous silicon, aluminum nitride, aluminum oxide, etc. Thisprinciple is illustrated in FIG. 1. The aforementioned layers can alsoprovide an electrical charge which introduces a repelling force, whichreduces the availability of carriers of the opposite polarity torecombine, thereby reducing recombination rates. The most prominentexamples of charge carrying passivating layers are silicon nitride andaluminum oxide. Another method of reducing the amount of carriers of onetype close to the surface is the diffusion of doping atoms either of thesame or the opposite doping of the wafer doping type. In this casedoping levels in excess of the wafer doping are necessary to obtain ahigh-low junction (also commonly called back surface field or frontsurface field) or a p-n junction. This can be combined with othermethods of surface passivation mentioned above.

High efficiency solar cells require good surface passivation combinedwith a technique to make electrical contact to the substrate withminimal recombination losses. Exemplary solar cell structures andpractical methods of forming the same, addressing the issues above, arethe subject of this invention.

SUMMARY OF THE INVENTION

The shortcomings of the prior art are overcome and additional advantagesare provided by the present invention, including solar cell structuresand formation methods which utilize the surface texture in conjunctionwith the passivating dielectric layer to provide a practical andcontrollable technique to form an electrical contact between aconducting layer and substrate through the passivating dielectric layer,thus achieving both good surface passivation and electrical contact withlow recombination losses, as required for high efficiency solar cells.One method of formation, and resulting structures, are illustrated in,e.g., FIGS. 2-3.

Also disclosed is a technique to produce a controlled-thin-dielectriclayer, which allows passage of majority carriers, but blocks themigration of substrate minority carriers to the conducting layer,thereby minimizing carrier recombination losses. This is illustrated in,e.g., FIGS. 6 and 11.

Also disclosed is a practical and controllable technique to create ahigh efficiency solar cell by injecting dopants through small openingsin a passivating dielectric layer into a semiconductor substrate toproduce a P-N junction buried beneath a passivating dielectricinterface. This results in a junction formed within the substrate (e.g.,bulk silicon), below a passivating layer with a low interface statedensity, thus resulting in low carrier recombination. This isillustrated in, e.g., FIGS. 9-11.

Furthermore, by injecting dopants through a controlled contact area, agradient dopant concentration can be formed within the contact opening.This dopant gradient is effective at repelling one polarity of carriers,thus resulting in a shielded low-carrier recombination contact. This isillustrated in, e.g., FIGS. 10-11.

Using textured substrate surface features in conjunction with adielectric passivation layer is a practical technique to control thetotal area of direct-contact, or alternatively, the thickness of thetunnel dielectric barrier contact between the conductive layer and thesubstrate. Moreover, a gradient dopant profile is formed through thecontrolled contact areas in either case. All of these functions areuseful in the fabrication of high efficiency solar cells. The principlesfor the control of the contact area are illustrated in, e.g., FIGS. 4, 7and 8.

In summary, the present invention includes, in one aspect, a shieldedelectrical contact through a passivating dielectric layer in ahigh-efficiency crystalline solar cell, in which the passivatingdielectric layer is substantially continuous over a substrate except atcontrolled contact openings on geometrical texture structures of thesubstrate. For example, the invention includes controllably providingthe controlled contact openings within the dielectric layer byselectively eroding the dielectric layer.

In one aspect, a P-N junction is formed in a substrate beneath thepassivating dielectric layer; by, e.g., diffusion or injection ofdopants from a dopant-containing conductive layer through the controlledcontact openings in the passivating dielectric layer.

Further, additional features and advantages are realized through thetechniques of the present invention. Other embodiments and aspects ofthe invention are described in detail herein and are considered a partof the claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in connection with the accompanying drawings in which:

FIG. 1 depicts in schematic form certain requirements of a highefficiency solar cell;

FIGS. 2 a-b are partial cross-sectional views of an exemplary solar cellwith a controlled contact structure, in accordance with one or moreaspects of the present invention;

FIGS. 3 a-e depict an exemplary process flow and resultant structuresfor shielded electrical contacting through a passivating dielectriclayer, in accordance with one or more aspects of the present invention;

FIGS. 4 a-b are partial cross-sectional views showing a controlledcontact opening through a dielectric layer realized by adjusting etchparameters to achieve desired contact opening area and profile, inaccordance with one or more aspects of the present invention;

FIG. 5 depicts preferential erosion of the dielectric layer at thepeaks, in accordance with one or more aspects of the present invention;

FIGS. 6 a-c depict exemplary contact structures formed including directcontact or tunnel barrier contact, in accordance with one or moreaspects of the present invention;

FIGS. 7 a-b depict contact area control, in accordance with one or moreaspects of the present invention;

FIGS. 8 a-b depict an alternative contact opening method using inducedcracking of the dielectric layer at the interface planes and peaks toachieve a preferential etch path for the contact opening, in accordancewith one or more aspects of the present invention;

FIGS. 9 a-b depict forming a P-N junction beneath a passivatingdielectric layer, in accordance with one or more aspects of the presentinvention;

FIGS. 10 a-d depict a shielded direct-contact structure realized inaccordance with one or more aspects of the present invention;

FIGS. 11 a-d depict a shielded tunnel barrier contact structure realizedin accordance with one or more aspects of the present invention; and

FIG. 12 is a partial cross-sectional view of an exemplary solar cellhaving multifunctional layers requiring electrical contact, inaccordance with one or more aspects of the present invention.

DESCRIPTION OF THE INVENTION

As shown schematically in FIG. 1, high efficiency solar cells requireboth low recombination current (Jo) and low contact resistance (Rc)between the substrate and conductive layers. A structured interfacelayer with e.g., 99.5-95% dielectric area and 0.5-5% contact areaachieves this requirement.

FIGS. 2 a-b are partial cross-sectional views of an exemplary solar cellwith a controlled contact structure in accordance with one or moreaspects of the present invention, in which a high efficiency solar cell10 provides both well passivated surfaces combined with low contactresistance between the conductive layer 11, metallization 14, and thesubstrate 13. A structure which utilizes a dielectric layer 12 topassivate the surface while providing for a relatively small area ofcontact between the conductive layer and the substrate is an idealstructure for high efficiency.

The shielded contact structure described herein is equally suited foruse as a front surface structure, as well as a back surface structure 8,or both as simultaneous structures in a high efficiency solar cell.

FIGS. 3 a-e depict an exemplary process flow and resultant structuresfor shielded electrical contacting through a passivating dielectriclayer, in accordance with one or more aspects of the present invention.

The process steps are discussed in further detail below, and may include(but are not limited to):

Step 21: Providing a substrate. The term “substrate” is used broadlyherein to connote any underlying layer or layers to which a conductiveconnection is required. Therefore, the cell structures herein couldinclude additional, underlying functional layers.

Step 22: Texturizing the substrate-texture (e.g., pyramid peaks) isetched into the substrate to form the base-structure for formingcontrolled contact areas between the substrate and subsequentlydeposited conductive layer.

Step 23: Depositing, growing, or otherwise forming a dielectric layerover the texturized substrate—to passivate the substrate and allow forcontrolled contact between the substrate and the subsequently depositedconductive layer.

Step 24: Opening contacts through portions of the dielectric layer.Contact openings are, e.g., eroded or etched along intersecting planesof the pyramid structure and/or through the peaks of the dielectriclayer to form controlled contact openings between the substrate and thesubsequently deposited conductive layer.

Step 25: A conductive layer is deposited on the upper surface and overthe controlled-contact-openings, forming a controlled-contact structurebetween the substrate and conductive layer.

Step 26: Diffusing dopants into the substrate if desired (discussedfurther below).

FIGS. 3 b-e show perspective views of the texturized structuresresulting from steps 22-25 above, respectively, in the case of pyramidtexture shapes. FIG. 3 d shows exemplary openings at the peaks and/oralong intersecting-planes of the pyramids.

FIGS. 4 a-b are partial cross-sectional views showing a controlledcontact opening through a dielectric layer 42 over a substrate 43,realized by adjusting etch parameters to achieve desired contact openingarea and profile, in accordance with one or more aspects of the presentinvention. Erosion of the intersecting-planes and/or peak areas of thetexture surface can be achieved by increasing the directionality of theion bombardment 46 through several techniques, including:

1. Increasing the strength of the attracting electrical field at theintersecting planes and peaks of the pyramids by introducing a charge inthe substrate through introduction of a DC or RF bias 48 at thesubstrate (e.g., FIG. 4 b).

2. Using a less-reactive gas species in the plasma, increasing erosiondue to direct ion bombardment over chemical etching.

3. Reducing the gas pressure, thereby increasing the ion mean free path.

FIG. 5 depicts preferential erosion of the dielectric layer 52 at thepeaks, in accordance with one or more aspects of the present invention.Charge density 56 is highest at the intersection of geometrical planesand peaks because on the lateral walls of the pyramid (or othergeometrical structure), the repulsive forces of the like-negativecharges lie in the plane of the surface, but near sharp intersections oftwo or more planes or especially at more than three planes forming apeak, the net negative force will be stronger and perpendicular to thesurface. As a result, the positive ions emitting from the plasma bombardpreferentially on the pyramid plane intersections or peaks due to thestronger attraction between the positive ions and the stronger negativecharge at the intersections and peaks.

The passivating dielectric layer erodes preferentially at the peak, dueto several factors, including electrical field strength at the peak,stress cracking at the peak, ion bombardment directionality, greatergeometrical exposure of the peak, etc.

FIGS. 6 a-c depict exemplary contact structures formed including directcontact 65 or tunnel barrier contact 66, in accordance with one or moreaspects of the present invention.

In FIG. 6 b, the passivating dielectric layer 62 can be eroded all theway through to make a direct contact opening. Alternatively, in FIG. 6c, the passivating dielectric layer 62 can be preferentially thinned atthe peak to form a tunneling dielectric barrier contact 66.

FIGS. 7 a-b depict contact area control, in accordance with one or moreaspects of the present invention. As the peaks are eroded vertically(Y), the 2-dimensional open contact area through passivating dielectriclayer 72 increases (X). Alternatively, the passivating dielectric layercan be preferentially thinned at the peak to form a tunneling dielectricbarrier contact, with control of “effective” contact area.

FIGS. 8 a-b depict an alternative contact opening method using inducedcracking of the dielectric layer 82 at the interface planes and peaks toachieve a preferential etch path for the contact opening, in accordancewith one or more aspects of the present invention.

Stress cracks 85 in the dielectric layer can be introduced topreferentially etch along the crack interfaces in a reactive ion etchprocess. Stress cracks can be thermally induced or caused by otherstress at the intersection of interface planes or peaks. Stress atintersecting planes is intrinsically higher than on the plane surfacesand can be further increased through parameters of the dielectricdeposition process. Varying the concentration of reactive species anddirectionality of the ion bombardment 83 can adjust the contact openingprofile and area.

FIGS. 9 a-b depict forming a P-N junction 98 beneath a passivatingdielectric layer, in accordance with one or more aspects of the presentinvention. A P-N junction 98 formed beneath a passivating dielectriclayer by injecting solid-phase dopants 97 into the substrate from adopant-containing conductive layer 91 through the contact openings inthe dielectric layer. Under thermal diffusion, dopant atomspreferentially diffuse through the locations of thinned or erodeddielectric.

FIGS. 10 a-d depict a shielded direct-contact structure realized inaccordance with one or more aspects of the present invention. A shieldedcontact (one with low carrier recombination losses) can be formed byformation of a dopant concentration gradient 108 that transitions fromhigh concentration at the conductive layer 101 interface, to a lowconcentration at the P-N junction within the substrate 103 below thecontact area 105 formed by openings in dielectric layer 102. The dopantprofile shields the contact from excessive carrier recombination losses.As previously described, the shielded contact can be present at theintersection of two or more planes, preferably at the intersection ofthree or more, such as the peak of a pyramidal structure, as shown.

FIGS. 11 a-d depict a shielded tunnel barrier contact structure realizedin accordance with one or more aspects of the present invention. Ashielded contact can also be formed by not opening the dielectric layer112, but by thinning the dielectric to a desired thickness (can bebetween 5-50 Angstroms), which allows one carrier polarity to tunnelthrough while presenting a barrier to the passage of the carriers of theopposite polarity. This structure is referred to as a tunnel barriercontact 116. Optionally, a dopant gradient 118 can be formed bydiffusing dopants 117 through the tunnel dielectric structure fromconductive layer 111 to further shield the contact from recombinationlosses.

Details of exemplary methods for producing the aforementioned shieldedcontact structures are described in further detail below. Solar cellsubstrate surface texture commonly takes the form of a multitude ofeither regularly or randomly distributed micron-scale pyramidalstructures. Other texture morphologies, including conical spiked pointsor other sharply-raised crystalline substrate structures will workequally well. Surface texturization can be formed using any number ofwell-known processes including alkaline etch, which produce a pyramidalsurface which reflects the underlying substrate crystalline structure,acid etch, which produces an irregular, random conical spiked surfacestructure. In each case, the texture structures may be first coated witha thin (not necessarily uniform) insulating dielectric layer. Theconformal dielectric layer may be deposited through many techniquesincluding thermal oxidation, chemical vapor deposition, physical vapordeposition, etc. By preferentially eroding or etching the conformaldielectric layer either to a desired thickness or entirely off of thepeaks or tips of the surface texture, the underlying substrate is eitherelectrically or physically exposed through the conformal dielectriclayer, providing paths or openings which form the contacts between thecell substrate and a conductive layer that is subsequently deposited ontop of the dielectric layer. Eroding or etching of the dielectric layer,prior to the deposition of the conductive layer, can be performed usingseveral available semiconductor processing techniques, including plasmaReactive Ion Etch (RIE) process or in-situ, through ion bombardment froma plasma enhanced chemical vapor deposition process (PECVD), used todeposit the conductive layer onto the dielectric layer. Other directedenergy sources, such as a laser, could be employed to achieve selectiveerosion of peak areas of the surface texture structures, though in-situprocesses previously described are preferred. Several exemplarytechniques to preferentially erode or etch the pyramid peaks aredescribed below and in, e.g., FIGS. 3-9.

Control of the contact area through the dielectric may be achievedthrough a combination of the pyramid geometry, treatment of thedielectric layer, and the intensity and directionality of the ablatingenergy, as follows:

1. The peaks of the pyramidal or conical-spike texture will erode oretch preferentially relative to the walls and base areas due to severaleffects. The peaks are more broadly and directly exposed to the etchingor eroding energy from a plasma or ion beam.

2. The pyramid shaped texture becomes progressively more truncated as anincreasing amount of material is etched from the peak. This is becauseof the increasing cross-sectional area of the base compared to the peakof the pyramid. In doing so, the contact opening through the dielectriclayer and into the substrate progressively increases. This progressivelyincreasing contact area allows one to control the amount of totalcontact area that has been opened between the conductive layer and thesubstrate to a desired amount. Increasing the duration and/or intensityof the etch/ion bombardment may be used to control the contact openingarea.

3. Inducing a net charge into the substrate, charges will migrate awayfrom like charges, thus repelling the charge to the extremities of thesubstrate surface, hence the charge density will tend to be highest atintersections of several surface planes, such as is the case of a peakof a pyramid shape or tip of a conical-spike structure. The elevatedcharge density at such peaks creates a stronger electrical field at thepeaks, which attracts a higher flux of ion bombardment than thesurrounding areas of lower charge density. Hence, the higher flux of ionbombardment results in a higher etch rate of the dielectric layer at thepeaks of such structures. The charging effect can be enhanced furtherthrough the use of a DC or RF bias into the substrate. Specifically,this can be achieved in parallel plate plasma reactors in which avoltage bias, either as DC or RF, is applied to the plate which is incontact with the substrate.

4. Thermally induce stress cracks into the dielectric film prior tosubjecting the substrate to a plasma, thereby preferentially etchingalong the stress crack interfaces through the dielectric layer. Surfacetexture structures have larger cross-sectional area at the base and cometo a point area at the peaks. This characteristic geometrical shape isused to provide a method to control the contact area relative to overallpassivated surface area.

5. Controlling the plasma etch conditions which affect the ionbombardment energy, direction, reactivity and time. These parameters arereadily controlled in modern plasma reactors such as PECVD, or PlasmaEtch chambers. FIGS. 4-6 illustrate (by way of example) the conceptsdescribed to control the ion bombardment directionality. Alternatively,other methods that utilize an energetic beam source, such as electronbeam, ion-beam, laser etc., could be applied. FIGS. 3 a-e illustrate theconcept of using the texture structure and a technique of making amultitude of contacts of a controlled cross-sectional area, between aconductive layer which is deposited continuously over the dielectric.

In all of the aforementioned structures, shielded electrical contact maybe made to the substrate 1) as a controlled-area direct contact betweenthe conductive layer and the substrate, and/or 2) via majority carriertransport through a controlled-thin-dielectric tunneling barrier. Thesetwo basic contact structures are illustrated in FIGS. 6, 10 and 11.

In the case of the direct contact, the completed cross-sectionalstructure is comprised of a stacked layer starting from a texturedcrystalline solar cell substrate with a multitude of electricallyconductive contacts passing through a passivating dielectric layer to anupper electrically conductive layer. Because the texture on a solar cellsubstrate is comprised of millions of uniformly distributed pyramids orconical spikes across the entire surface of a solar cell substrate, thisstructure and method provides a technique of forming well-distributedcontacts of a controlled cross-sectional area between the substrate andconductive layer in a solar cell.

The structures that have been described herein minimize carrierrecombination in areas underneath the contacts through severaltechniques. One technique is minimizing the total contact area betweenthe conductive layer and the substrate relative to the total cell area,ideally to 0.5% up to 5%. Another technique is shielding the contacts byleaving a controlled-thin-dielectric passivation layer in place, relyingon tunneling current through the dielectric. A third technique isinjecting a high concentration of dopants through the relatively smallcontact areas, resulting in a high doping atom concentration at thecontact, which reduces recombination losses by reducing the number ofcarriers of the opposite charge in the vicinity of the contact.

In one embodiment, a solar cell substrate is first etched to form apyramidal surface texture. Next, the substrate is continuously coatedwith a dielectric passivation layer. Next, in-situ with and prior to thedeposition of a conductive layer, the dielectric layer is eroded fromthe peaks of the pyramidal texture micro-structure. Next, the dielectriclayer is coated with a dopant-containing conductive layer. Next, usingthermally activated diffusion, the dopants contained in the conductivelayer are injected through the field of controlled contact openingsformed in the dielectric layer at the eroded peaks of a pyramidal orspike-shaped textured surface profile. The dopants injected through thecontact openings diffuse into a continuous P-N junction within thesubstrate beneath the passivating dielectric layer. Low recombinationlosses is achieved by virtue of the very low total contact area relativeto the total passivating area (less than 5/100) combined with a gradientof dopant concentration within the contacts, which creates a chargepolarity which repels one polarity of carriers thereby reducingcarrierrecombination losses. The above-described embodiment of thisinvention is highly beneficial in the fabrication of high efficiencysolar cells. One embodiment of this is illustrated in FIGS. 9-11.

The shielded contact structure described herein is equally suited foruse as a front surface field as well as a back surface field, or both assimultaneous structures of a high efficiency solar cell.

In accordance with the above incorporated Applications entitled“High-Efficiency Solar Cell Structures and Methods of Manufacture”, acell comprising an n-type front, n-type wafer, p-type back,multifunctional transparent, conductive, highly doped silicon compound(or one of opposite polarity) can be used in combination with any of thecontact features of present invention. One embodiment of this is shownin FIG. 12, including the following exemplary layers:

124: Front metal contact

121: Transparent and conductive film:

Examples

amorphous or polycrystalline silicon carbides:

n-type silicon carbide: phophorus doped silicon carbide, nitrogen dopedsilicon carbide,

amorphous or polycrystalline silicon:

n-type amorphous silicon: phosphorus doped amorphous silicon, nitrogendoped amorphous silicon,

122: Electrically passivating interface layer;

Examples: silicon oxide,silicon nitride, amorphous silicon, siliconcarbide, aluminum oxide, aluminum nitride;

123: n-type crystalline silicon wafer

thickness is the range of w<300 um, base resistivity for n-type wafers0.5 Ohm cm<rho<10 Ohm cm, for p-type wafers 0.1 Ohm cm<rho<100 Ohm cm

222: Electrically passivating interface layer;

Examples: silicon oxide, silicon nitride, amorphous silicon, intrinsicsilicon carbide, aluminum oxide, aluminum nitride;

221: transparent and conductive film

Examples

amorphous or polycrystalline silicon carbides:

p-type silicon carbide: boron doped silicon carbide, aluminum dopedsilicon carbide, gallium doped silicon carbide, . . .

amorphous or polycrystalline silicon:

p-type amorphous silicon: boron doped amorphous silicon, aluminum dopedamorphous silicon, gallium doped silicon carbide, . . .

224: back metal

The layers described within the above solar cell structures can bedeposited or grown with standard methods like PECVD, APCVD, LPCVD, PVD,plating etc. For some layers and combinations of layers, innovativemethods of producing the layers and structures are necessary.

In order to achieve a highly efficient solar cell with a cost-effectiveproduction method, it is advantageous to deposit films of differentcharacteristics only on one side. While this is very hard to do, next toimpossible, for a standard tube furnace deposition of e.g. LPCVDdeposited polycrystalline silicon, a PECVD deposition can be done on oneside of a wafer without deposition on the other side. PECVD tools areavailable on industrial scale but they only operate in temperatureregimes where amorphous or microcrystalline silicon layers can bedeposited. In the described cell structures, amorphous silicon layerscan be turned into polycrystalline silicon layers by a thermaltreatment. This also holds for doped amorphous silicon layers orcompounds of amorphous silicon carbides, etc. This recrystallizationnegatively affects the passivation quality of the silicon/amporphoussilicon interface layer in case it exists in the cell structure.However, having an insulator buffers the wafer surface from thecrystallized polysilicon layer. This way the interface is stillpassivated after the thermal treatment and the layer systems arehigh-temperature stable. During the crystallization process manyproperties of the layer change: Donors or acceptors get activated, theoptical transmission increases, hydrogen effuses from the layer.

The present invention extends to any type of integrated, semiconductorcircuits having layers requiring conductive contact, in addition to thesolar cell examples disclosed herein.

In summary, certain aspects of the present invention include but are notlimited to:

A shielded electrical contact through a passivating dielectric layer ina high-efficiency crystalline solar cell, structure and methods ofmanufacture.

A shielded contact through a passivating dielectric that is formed bymodifying the geometrical features of surface texture formed on a solarcell substrate.

A shielded contact structure and method forming both a front surfacefield and/or a back surface field.

A contact structure and method in which the passivating dielectric layeris fully continuous over the substrate with the only exception being atthe controlled-contact openings on the geometrical texture structures.

A contact structure and method which can controllably achieve between0.5-5% total contact area by selectively eroding a dielectric layercoated on the surface texture of a solar cell substrate.

A contact structure and method which can controllably achieve between0.5-5% total contact area distributed at uniform overall density with acontrolled area coverage ratio across the surface area of a solar cellsubstrate by selectively eroding controlled areas of a dielectric layercoated on the geometrical surface texture of a solar cell substrate.

A contact structure and method which can controllably achieve between0.5-5% total contact area by selectively eroding controlled areas of adielectric layer coated on the geometrical surface texture of a solarcell substrate through plasma ion bombardment or reactive ion etching.

A contact structure and method which can controllably achieve between0.5-5% total contact area by selectively eroding controlled areas of adielectric layer coated on the geometrical surface texture of a solarcell substrate by directed ablation energy, such as LASER.

A shielded contact through a passivating dielectric that is formed bymodifying the geometrical features of surface texture on the solar cellsubstrate prior to deposition of a conductive layer.

A shielded contact through a passivating dielectric that is formed bymodifying the geometrical features of surface texture on the solar cellsubstrate in-situ with the deposition of a conducive layer.

A contact through a passivating dielectric that is formed by modifyingthe geometrical features of surface texture on the solar cell substrateby utilizing the geometrical shape of the texture structure to controlthe contact opening area in a dielectric layer.

A contact through a passivating dielectric in which the geometricalshape of the texture structure is larger at the base and converging to asharp peak or spiked-tip which allows the contact opening area to beprogressively increased as the peak or spiked-tip is progressivelyeroded off.

A contact through a passivating dielectric in which the geometricalshape of the texture structure is a pyramid shape, conical-spike orother structure monolithically protruding out of a crystalline solarcell substrate of less than 180-degree included angle.

A contact structure that is either a shielded-direct contact between asolar cell substrate and a conductive layer or a thin-dielectric tunnelbarrier contact.

A contact and method of manufacturing in which the contact opening areathrough a passivating dielectric is not highly dependent on having auniform height of the geometrical texture structures, including pyramidor conical-spike structures.

A contact structure and method in which a P-N junction is formed in asubstrate beneath a passivated dielectric layer.

A contact structure and method in which a P-N junction is formed in asubstrate beneath a passivated dielectric layer via diffusion orinjection of dopants from a dopant-containing conductive layer throughcontrolled openings in a passivating dielectric layer.

A contact structure and method that is either a shielded-direct contactbetween a solar cell substrate and a conductive layer or athin-dielectric tunnel barrier contact that is further shielded byinjection or diffusion of dopants from the conductive layer through thecontact opening or through the tunnel barrier into the substrate belowthe contact.

A contact structure and method that is further shielded by injection ordiffusion of dopants from the conductive layer through the contactopening or through the tunnel barrier into the substrate below thecontact forming a dopant concentration gradient within the contact.

A contact through a passivating dielectric that is formed bypreferentially eroding the dielectric layer at the peaks of thegeometrical features of surface texture due to greater physical exposureto the eroding energy, such as ion bombardment.

A contact through a passivating dielectric that is formed by modifyingthe geometrical features of surface texture on the solar cell substrateby utilizing an electric charge or electrical field that is concentrateddue to the geometrical shape of the texture structure to preferentiallyerode the dielectric layer over specific areas of the texturestructures.

A structure and method in which the dopant diffusion depth is greatestat peaks and intersecting planes, in comparison to flat surfaces andvalleys, thereby forming the P-N junction furthest away from said peaksand intersecting planes, hence contributing to a device with minimizedsurface recombination.

A contact through a passivating dielectric that is formed bypreferentially eroding the dielectric layer along the intersections oftwo or more geometrical planes of the surface texture structure on thesolar cell substrate by utilizing an electric charge or electrical fieldthat is concentrated due to the geometrical shape and electricalcharging capacity of the structure.

A contact through a passivating dielectric that is formed bypreferentially eroding the dielectric layer at the peak formed at theintersections of three or more geometrical planes of surface texture onthe solar cell substrate by utilizing an electric charge or electricalfield that is concentrated due to the geometrical shape of the texturestructure to preferentially erode the dielectric layer over specificareas of the texture structures.

Stress cracks in the dielectric layer introduced to enhance preferentialetching along the crack interfaces in a reactive ion etch process.

Stress cracks located at the intersection of two or more interfaceplanes or peaks due intrinsically higher stress at the intersection ofplanes and further increased through parameters of the dielectricdeposition process used to enhance preferential etching of the surfacetexture structures.

The process flows depicted herein are just examples. There may be manyvariations to these diagrams or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order, or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions and the like can bemade without departing from the spirit of the invention and these aretherefore considered to be within the scope of the invention as definedin the following claims.

1. A method of shielded electrical contact through a passivatingdielectric layer in a high-efficiency crystalline solar cell, in whichthe passivating dielectric layer is substantially continuous over asubstrate except at controlled contact openings on geometrical texturestructures of the substrate.
 2. The method of claim 1, furthercomprising controllably providing the controlled contact openings withinthe dielectric layer by selectively eroding the dielectric layer.
 3. Themethod of claim 2, further comprising controllably providing thecontrolled contact openings within the dielectric layer by selectivelyeroding controlled areas of the dielectric layer through plasma ionbombardment or reactive ion etching.
 4. The method of claim 2, furthercomprising controllably providing the controlled contact openings withinthe dielectric layer by selectively eroding controlled areas of thedielectric layer by directed ablation energy, such as laser.
 5. Themethod of claim 2, wherein the geometrical shape of the texturestructures is generally larger at the base and converging to a peak orspiked-tip which allows the contact openings to progressively increaseas the peak or spiked-tip is progressively eroded off.
 6. The method ofclaim 2, further comprising forming a P-N junction in a substratebeneath the passivating dielectric layer.
 7. The method of claim 6, inwhich the P-N junction is formed via diffusion or injection of dopantsfrom a dopant-containing conductive layer through the controlled contactopenings in the passivating dielectric layer.
 8. The method of claim 7,in which the dopant diffusion depth is greatest at peaks andintersecting planes of the texture structures forming the contactopenings, thereby forming the P-N junction furthest away from said peaksand intersecting planes, thereby providing minimized surfacerecombination.
 9. The method of claim 2, further comprising modifyingthe geometrical texture structures using an electric charge orelectrical field that is concentrated due to the geometrical shape ofthe texture structures to erode the dielectric layer over specific areasof the texture structures.
 10. The method of claim 9, wherein theelectric charge or electrical field is concentrated in certain areas dueto the geometrical shape and electrical charging capacity of thestructures.
 11. The method of claim 2, further comprising eroding thedielectric layer at peaks of the texture structures formed at theintersections of geometrical planes of the texture structures therebyeroding the dielectric layer over specific areas of the texturestructures.
 12. A solar cell formed according to the method of claim 2.13. A solar cell electrical contact structure for a conductive layerover a dielectric passivating layer, formed according to the method ofclaim
 2. 14. A shielded electrical contact through a passivatingdielectric layer in a high-efficiency crystalline solar cell, in whichthe passivating dielectric layer is substantially continuous over asubstrate except at controlled contact openings on geometrical texturestructures of the substrate.
 15. The method of claim 14, furthercomprising a P-N junction in a substrate beneath the passivatingdielectric layer.
 16. A solar cell formed according to the method ofclaim
 1. 17. A solar cell electrical contact structure for a conductivelayer over a dielectric passivating layer, formed according to themethod of claim 1.